1. Field of the Invention
This invention relates to a reproducing apparatus for reproducing information signals recorded in the form of oblique tracks on a magnetic tape by rotary heads.
2. Description of the Prior Art
In case of reproducing an information signal recorded on a tape in the form of oblique tracks, a reproducing apparatus performs helical scanning by rotary heads in general. In this case, the information signal recorded on the tape is segmented track by track. For example, in a reproducing apparatus for reproducing a video signal, such as the consumer use VTR (VHS or the like), the video signal is segmentally recorded on a tape to form one track by one field and two tracks by one frame. This tape has a control (CTL) signal (one pulse per one frame) recorded on a track (linear track) formed in the lengthwise direction of the tape independently of the oblique track. This CTL signal is used during reproduction to control tracking so that each head can scan the corresponding tracks properly. In this case, the frame of the information signal to be reproduced from the tape is required to be synchronized with a reference frame signal. For example, in the pre-roll period of assembly editing, the control signal reproduced from the tape is compared in phase directly or indirectly with an external reference frame signal, and the result thus compared is reflected to the tracking control, so that the frame of the reproduced signal is synchronized with the external reference frame finally.
With the conventional reproducing apparatus as described above, since each frame is composed of two tracks which are different in azimuth from each other, the frame synchronization also can be performed simultaneously by effecting the tracking control using the tracking signal (in this case, CTL signal) without special frame information. However, if the number of tracks per frame is made larger than two, the reproduced frame cannot be synchronized with the reference frame by this method which does not have any synchronization information signal other than the CTL signal for tracking.
With a D-1 digital VTR, one frame signal is segmented into 20 to 24 tracks to be recorded on a tape. In this case, the linear track (control track) exists, and one pulse servo signal per one rotation of a drum (four tracks) and one pulse frame signal per one frame are recorded on the tape. For effecting the external synchronization, the same control as that with the consumer-use VTR described shown above may be effected using the frame signal (see, for example, journal of "Hoso-Gijutsu (Broadcasting Technologies)" Vol. 43, No. 12, 1990).
A method of effecting the tape editing using a time code in the industrial-use VTR is disclosed in U.S. Pat. No. 4663679. According to this disclosure, a time code signal showing the address of information recorded on a tape is recorded on the tape independently of the CTL signal. The reproducing apparatus compares the time code signal read out from the tape and a reference time code signal, controls the tape feeding so as to synchronize the time code signals with each other, and then executes the tracking control using the CTL signal. The time code signal shown in this example is a series of numerical information which are increased (or decreased) monotonously. On the other hand, the above-mentioned frame has a constant period. As a result, in this example, with respect to the above-mentioned problem, the objects to be synchronized with each other are different in periodicity. However, this method offers one solution to the problem.
In the conventional reproducing apparatus explained above, the information unit to be synchronized, namely, the frame signal period and the tracking signal (in the example, CTL signal) period are selected such that one becomes an integral multiple of the other. Accordingly, as seen in the consumer-use VTR shown above, when the frame signal period is equal to or smaller than the tracking signal period, the frame synchronization is attained simultaneously by effecting the tracking control. On the other hand, when the frame signal period is larger than the tracking signal period, the tracking control may be effected after the frame of the reproduced signal has been synchronized with the reference frame signal. However, if one of the frame signal period and the tracking signal period is not an integral multiple of the other, such a situation will occurr in which the tracking control cannot be effected stably at the position where the frame synchronization is attained.
In addition, since both CTL and frame signals are recorded on the linear track, the reading period becomes longer, so that both the tracking control and frame phase control are difficult to carry out at a high response speed. This means that a long period of time is required to attain the frame synchronization.